Trenchless Technology Rehabilitates Colorado Culverts

Stacked concrete pipes abstractA new project that has been slowly accepted by state departments of transportation has found its way to Colorado.

Centrifugally cast concrete pipe (CCCP) is a trenchless rehabilitation technique, used in large sewers and culverts. Led by the Colorado Department of Transportation (CDOT), the new project to rehabilitate culverts is groundbreaking.

“There were a total of 10 large culverts in this particular project (CDOT #20158R, Region One, covering the Greater Denver Metro and Central Colorado area) and seven seemed like good candidates for CCCP,” Paul Snyder, who is president of American West Construction LLC (AWC), tells TrenchlessOnline.com. “And since specifications were written in a way that permitted CCCP, we went for it — it’s the largest CentriPipe project in Colorado, so far.”

AP/M Permaform developed the CentriPipe technology. It is done by using a spincasting sled inserted through a pipe. The sled is then withdrawn as an operator sprays thin and even layers of a cement mortar along the walls of the sewer or culvert.

That mortar is then used as a new pipe that is now structurally sound and rests within the old culvert; the new pipe is durable and waterproof and is completely independent of the original pipework. The competition’s solutions all require much larger staging than this new technology.

Work has been completed, as of July 2015, on four out of seven culverts. Only one of the culverts has given the team an issue so far.

“[The section of] 460 ft of 48-in. CMP, with complications, was a big project for us, approaching the maximum that we’re able to undertake successfully with our current setup,” Snyder says. “But, on the other hand, we learned a lot about what can be done with CCCP, and I’m looking forward to projects that are even bigger and more challenging.”

Those complications were due to an embankment being where the team needed to stage along with groundwater continuously entering the culvert as they worked.

“The staging area on the embankment meant that we had to pump down, then up plus, of course, we were pumping through nearly 500 ft of hose, all of which added significant pumping load. But ultimately, we were able to do what we needed to do with our standard pumps,” Synder says.

To begin putting in the new pipe, a process of dewatering the existing pipe has to happen, which was tricky with this particular culvert.

“First, we diverted water entering into the culvert, but that still left a lot of high groundwater entering through the culvert walls,” Snyder explains. “So, we dug a sump into the culvert and pumped from there. That meant we had to run hose back along the floor of the pipe, which we had to adjust and work around for the first couple of runs. After that, the early layers held out the groundwater, and we were working in a dry culvert for the final runs.”

Six passes were needed to complete the work on that culvert, and the teams say the others have needed at least four. CentriPipe was a blessing in these projects though, because they only need small staging areas. In Region One of the CDOT, there is steep terrain, which would have made it difficult, if not impossible, to rehabilitate the culverts.

“We can work from a trailer that carries the mixer and pumps we need, and it isn’t a huge trailer,” Snyder says. “That was great generally — for one thing, these culverts are spread over a big area, and it’s nice to be able to move from site to site more easily. And, on at least a couple of sites, I’m sure we would have needed additional construction easements to do the work, and it’s good for drivers and everyone else if we can avoid that.”

No road closures were necessary for any of these projects, and none are expected in the remaining work to be done. Snyder says he is pleased with the projects so far.

“This is one of our first CentriPipe projects, and we learned a lot,” he says. “But all in all, we’ve been able to work efficiently, and I like to crawl back into the newly rehabilitated culverts and take a look — the quality and strength of this process is obvious.”

New trenchless technology to work on sewers is integral to solving many of the issues the nation still faces.

At the end of September, an International Construction and Utility Equipment Exposition showed off numerous groundbreaking improvements on trenchless technology, and they will likely make their way through the industry in the coming year. Many are still unaware of the technology’s existence, even though trenchless tech has been around for 15 years.

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